Oxidation-resistant coatings for ultra-high-temperature refractory Mo-based alloys

The synthesis of robust coatings that provide protection against environmental attack at ultra-high temperatures is a difficult challenge. In order to achieve this goal for Mo-based alloys the fundamental concepts of reactive diffusion pathway analysis and kinetic biasing are used to design a multilayer coating with a phase sequencing that provides for structural and thermodynamic compatibility and an underlying diffusion barrier to maintain coating integrity. The coating structure evolution during high-temperature exposure facilitates a prolonged lifetime as well as a self-healing capability. Both borosilicide and aluminide coatings that can be synthesized by a pack cementation process are demonstrated to yield superior environmental resistance on Mo-based systems at temperatures up to l,700A degrees C and can be adapted to apply to other refractory metal systems.